Lattice fin for missiles or other fluid-born bodies and method for producing same

ABSTRACT

A method for the manufacture of lattice fins for fluid-born bodies is provided. In one embodiment, lattice fins having a metallic cell structure are manufactured from strips or sheets of metal. In another embodiment, composite lattice fins are manufactured from a log assembly of elongated mandrels covered with a fiber reinforced composite material. After curing, individual fins are sliced from the log assembly. Upon removal of the mandrels, a cell structure is obtained. Combinations of the two embodiments are also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.Provisional Application No. 60/337,318, filed on Dec. 6, 2001, and60/422,012, filed on Oct. 29, 2002, the disclosures of which areincorporated by reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The work leading to the invention received support from the UnitedStates federal government under SBIR Grant, Contract Nos.F08630-01-C-0029 and F08630-02-C-0014. The federal government may havecertain rights in this invention.

BACKGROUND OF THE INVENTION

Many air-to-air and air-to-ground, powered and unpowered, guided andunguided munitions have a common feature—fixed, conventionally-shapedairfoil section fins to stabilize and direct the flight path afterseparation from an aircraft. These weapons, such as the MK80 family of“dumb” bombs and the AIM-9 air-to-air missile, are usually carried bytactical aircraft as external stores, where space for fixed fins iscomparatively plentiful, and the range, speed, and radar cross sectionpenalties associated with external carriage are tolerated.

External weapons carriage is a major source of drag and greatlyincreases radar reflection. Increasing emphasis on stealth technologyincreases the need for future air-launched weapons, sensors, and cargoof all types to be designed for internal carriage. Folding fin systemsare one important approach to diminishing the stowed volume of theseinternally carried payloads. Internal payload carriage also demands morecompact fin configurations. The same technology is similarly useful forany tube or gun launched, guided or unguided projectile or vehicle.

Traditionally, the US military has employed two basic types of foldingfin systems. In a first type, airfoil-shaped fins are stowed so thatthey snap open in a direction parallel to the flight path. In a secondtype, side-deploying fins wrap around the circumference of the body ofthe weapon to minimize undeployed volume required for storage duringtransportation.

The Russian military has deployed several operational ballistic orair-to-air missile systems using an effective fin technology that isdifferent in configuration and operation than any preceding deployablefin system. Termed a “gas dynamic declination device” by the Russians,and a lattice or grid fin in the US, this system consists of severalessentially rectangular “paddles” filled with a grid of approximatelytriangular, square, and diamond-shaped cells formed by a cross-hatchingof thin metal. The fins are fixed to the missile body at the root end ina manner that allows them to be folded flat against the body of themissile in storage. Upon launch, the fins are deployed with their broadlattice face perpendicular to the missile body axis, and may be attachedto internal mechanisms that allow the fin to be moved for directionalcontrol of the payload. Deployment is reliable because air loads on thefin are usually in the direction of desired motion, up and to the rear,although springs or other devices may be used to assure or hastendeployment.

The US has undertaken an extensive evaluation of the lattice or grid finconcept. The first US patent on grid fin technology, U.S. Pat. No.5,048,773, issued in 1991 and is held by the U.S. Government. There is aRussian patent claim for use of these devices in supersonic poweredrockets such as the AA-12. Fulghum, David, “Lattice Fin Design, Key toSmall Bombs,” Aviation Week & Space Technology.

Numerous aerodynamic and systems studies, most notably by Mark Millerand David Washington, have been conducted over the past ten years.Miller, M. and Washington, D., “An Experimental Investigation of GridFin Design”; Miller, M. and Washington, D. “An ExperimentalInvestigation of Grid Fin Drag Reduction Techniques”; and Miller, M. andWashington, D., “Grid Fins-A New Concept for Missile Stability andControl.” These studies have shown that lattice fins are aerodynamicallyeffective control surfaces that have slightly higher drag thanconventional airfoil fins. If increasing priority is given to compactstorage, lattice fins have an advantage over conventional systems. Theyoffer interesting secondary advantages as well. They can operate at highangles of attack without flow separation because the multiple channelsof the lattice act as guides controlling the flow. Because of theirsmall size and small center-of-pressure travel with large changes ofangle of attack, actuator size and power for controllers can be greatlyreduced, leaving more space in an air-born system for fuel and otheruseful payload. Perhaps more importantly for internal carriage, latticefins allow an air-born payload to maintain similar capability in asmaller package compared to a conventionally finned payload.

The fluid dynamics and performance of lattice fin-equipped bombs,rockets and missiles and other payloads have been extensively studiedboth analytically and experimentally for a decade. However, thestructure of lattice fins has not significantly changed from the steelconfiguration mentioned in the US Government's 1991 patent on thistechnology. Operational Russian fins, as well as almost all USexperimental lattice fins, have been built from metals to help themresist the high stagnation temperatures of supersonic flight.

Prior art steel lattice fins are expensive to make. These lattice finsare machined from a solid block of metal by electrical dischargemachining (EDM) or water jet cutting. Air Force estimates of the cost ofa stainless steel lattice fin made by EDM are approximately $2000. Thisprice is beyond the level of reasonableness for many of the more“routine” and expendable classes of the payloads. Thus, a morecost-efficient lattice fin and method for its production are desirablefor this technology to transition from a special purpose laboratorycuriosity to a widely used performance enhancement.

SUMMARY OF THE INVENTION

The present invention provides a more cost efficient approach to themanufacture of lattice fins for fluid-born bodies. In one embodiment,metallic fins are manufactured using metal in sheet or strip form. Inanother embodiment, composite fins are manufactured from a log assemblyof wrapped mandrels, individual fins being subsequently sliced from thelog assembly after curing. Combinations of the two techniques are alsouseful.

In the metal lattice fin, strips of slotted metal are assembled in anegg crate fashion or bent to form a stair step to provide a cellstructure. An outer frame is provided around the cell structure. Theresulting assembly is fastened and solidified by, e.g., brazing,welding, or adhesive bonding. An attachment base or yoke is formed andattached to the cell structure.

In the composite fin, a fibrous reinforcement, either dry orpre-impregnated with a matrix material, is wrapped around elongatedmandrels. The mandrels are assembled into a log, infused with the matrixmaterial if necessary, and cured. The resulting log is transverselysliced to provide individual lattice fins. The slices need not beperpendicular to the longitudinal axis of the log, but can be contouredin any desired manner, for example, to fit against the curvature of thefluid-born body. Manufacturing the lattice structure in this mannerallows recurring manufacturing costs to be spread over many finishedparts.

DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood by reference to thefollowing detailed description when considered in conjunction with theaccompanying drawings, in which:

FIG. 1 is a perspective view of one embodiment of a lattice finaccording to the present invention;

FIG. 2 is a front view of the lattice fin of FIG. 1;

FIG. 3 is a side view of the lattice fin of FIG. 1;

FIG. 4 is a top view of the lattice fin of FIG. 1;

FIG. 5 is a perspective view of a metal interior cell structure formedfrom metal strips for a lattice fin embodiment under construction;

FIG. 6 is a perspective view of a metal outer frame formed from metalstrips for a lattice fin embodiment under construction;

FIG. 7 is a partial plan view of one embodiment of a metal strip for themetal interior cell structure;

FIG. 8 is a partial plan view of a further embodiment of a metal stripfor the metal interior cell structure;

FIG. 9 is a cross-sectional view of a single metal strip for the metalinterior cell structure illustrating shaping of the leading and trailingedges;

FIG. 10 is a schematic view of a step of bending metal strips to form aninterior cell structure according to a further embodiment of theinvention;

FIG. 11 is a schematic view of a step of expanding strips of metal toform an interior cell structure according to a still further embodimentof the invention;

FIG. 12 is a schematic diagram illustrating steps in the process offorming a lattice fin from a composite material according to a furtherembodiment;

FIG. 13 is a schematic isometric diagram illustrating a tooling assemblyfor use in the process of FIG. 12;

FIG. 14 is a perspective view illustrating mandrel alignment buttons foruse with the tooling of FIG. 13;

FIG. 15 is a perspective view illustrating mandrel alignment end platesfor use with the tooling of FIG. 13;

FIG. 16 is a perspective view of a vacuum bagging process for forming alattice log structure according to a further embodiment of the presentinvention; and

FIG. 17 is a perspective view of a metal lattice fin according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a lattice or grid fin 10 having aninterior cell structure 12 and a surrounding outer frame 14, illustratedgenerally in FIGS. 1-4. A base 16 is attached to or formed integrallywith the frame at one end. The base is configured for pivotingattachment to a missile or other fluid-born body, and possibly also forlater directed motion of the fin to control the path of the body. Thoseof skill in the art will appreciate that the particular design of thelattice fin, for example, the dimensions of the fin and the number,shape and configuration of cells in the cell structure, can varydepending on the intended application. The present methods ofmanufacturing a lattice fin are applicable regardless of the particularfin design.

According to the present invention, the lattice fin may be formedentirely of metal, entirely of a composite material, or may be a hybridof metal and a composite material. A hybrid embodiment may have theinterior cell structure 12 formed of metal with the outer frame 14formed of a composite material, or the interior cell structure 12 formedof a composite material with the outer frame 14 of metal. In anyembodiment, the base 16 may be formed of either metal or a compositematerial. Additionally, in any embodiment, a thicker shell of materialcan be added to the perimeter of the lattice grid or fin to increasestrength and stiffness, as well as to protect the interior cellstructure.

In a first embodiment, the lattice fin is made entirely of metalprovided in sheet or strip form. That is, both the outer frame and theinterior cell structure are made of metal. The choice of metal dependson factors such as the conditions of use and cost. For example,stainless steel or titanium may be used for high temperatureapplications, such as supersonic flight. Aluminum may be used for lowertemperature applications, such as subsonic or transonic flight.

In one embodiment, referring to FIGS. 5-8, the interior cell structure12 is made from a plurality of elongated metal strips 20 having twoopposed long edges 21, 23. The strips are slit at intervals for assemblyin an egg crate fashion. The slits 25 can extend alternately from eachlong edge 21, 23 to the middle of the strip, as best seen in FIG. 7, oralternatively, can extend only from a single edge, e.g., edge 23, asbest seen in FIG. 8. The distance between slits is chosen based ondesired cell geometry, and may vary along the length of the strip toproduce differing cell shapes in a grid if desired. The width of theslit is slightly more than the thickness of the strip with which itmates, to allow the two parts to slide into each other. When assembled,the slits 20 intersect to form joints 30 between the cell walls (seeFIG. 2). The slits can be made in any suitable manner, such as by lasercutting, water jet cutting, sawing, machining, or any other mannerapparent to those of skill in the art.

Any configuration of cells can be provided, depending on theapplication. The length of the strips and location of the slits dependson the particular cell configuration desired. In a suitable embodiment,the length of each strip is a multiple of the length of a cell wall plusa sufficient amount at one or both ends to form a bend 32 for attachmentto the outer frame or to an adjacent strip. For example, in theconfiguration illustrated in FIG. 5, four strips 22 have a lengthsufficient to form three adjacent cell walls. Four strips 24 have alength sufficient to form five adjacent cell walls. Four strips 26 havea length sufficient to form six adjacent cell walls.

After assembly into the cell structure, the strips are fastened to eachother in any suitable manner, as by brazing, welding, or bonding, sothat the cell structure becomes an integral piece. A further metal strip40 (see FIG. 6) is wrapped around the entire cell structure to form theouter frame. The outer frame is attached to the cell structure in anysuitable manner, such as by brazing or welding. The cell structure andouter frame may be attached together in a single operation, for example,by furnace or dip brazing. Alternatively, the outer frame may beattached to the cell structure after the cell structure has beenfastened together. In a still further embodiment, the strips of the cellstructure may be configured to form an outer frame integrally with thecell structure.

In another embodiment, the metal cell structure is overwrapped with acomposite material that forms the outer frame 14. The composite materialis formed from a uni-directional or multi-directional fibrousreinforcement impregnated with a matrix material. The fibrousreinforcement may be supplied initially in any suitable form, such asindividual tows of continuous or spun fiber or yarn from spools,unidirectional tape, broadgoods formed of fibers that are woven, pliedwith perpendicular or other intersecting angles, nonwoven, or knitted,or in any other suitable form known in the art. The fibrousreinforcement, either dry or pre-impregnated with a matrix precursormaterial, can be wrapped around the metal cell structure, infused with amatrix precursor material if necessary, and cured in place, which alsobonds the fabric to the metal. Alternatively, the composite frame can bemolded independently and subsequently bonded to the metal cellstructure. Any suitable structural adhesive that is capable ofwithstanding the intended operating temperatures can be used.

The lattice fin is frequently shaped to minimize drag. Toward this end,the strips 20 are made as thin as possible, while still providingsufficient strength to withstand the manufacturing process and theconditions of use. For example, stainless steel strips can be made asthin as 0.005 inch. A greater thickness may be acceptable, depending onthe application.

As a further way to reduce drag when such is desirable for a particularapplication, the strips 20 can be shaped on one or both edges 21, 23 toa double bevel or other aerodynamically appropriate shape 42, 44 toprovide an aerodynamic profile for reducing drag. See FIG. 9.Preferably, at least the edge forming the leading edge of the latticefin when in use is shaped. The lowest drag results when both the leadingand trailing edges are shaped. Preferably, the strips are shaped priorto slitting and assembly into the cell structure. The strips can beshaped in any suitable manner, such as by the sharpening process usedfor razor blades.

In another embodiment, the cell structure is fabricated as a lattice bybending metal strips of the appropriate width to provide the desiredconfiguration. See FIG. 10. The bent strips are assembled and welded orotherwise fastened together at their points of contact. In a furtherembodiment, a lattice structure is created by welding strips of metaltogether at alternate locations and expanding the strips. See FIG. 11.This produces a lattice with thicker walls at the points of attachment.An outer frame of metal or composite material is wrapped around theperimeter of the cell structure, as described above.

In still another embodiment, the cell structure 12 is formed from sheetmetal stock formed over mandrels into tubing, which can be square,round, or another appropriate cross-sectional shape. The tubes are thenstacked and brazed or welded together at their contact points to form along lattice log structure. The log is then sliced into fins of theappropriate width. The tubes can have different geometries or walllengths, to provide any desired configuration for the finished grid,once assembled. An outer frame of metal or composite material isprovided around the perimeter of the cell structure, as described above.

In a further embodiment, the interior cell structure 12 is formed from acomposite material comprising a unidirectional or multi-directionalfibrous reinforcement impregnated with a matrix material. Suitablefibers include carbon, boron, Aramid, ceramic, and glass fibers,nano-fibers, and other structural reinforcement fibers known in the art.The fibrous reinforcement may be supplied initially in any suitableform, such as individual tows of continuous or spun fiber or yarn fromspools, unidirectional tape, broadgoods formed of fibers that are woven,plied with perpendicular or other intersecting angles, nonwoven, orknitted, or in any other suitable form known in the art. Suitable matrixmaterials include resins such as epoxy, polyester, vinyl ester,phenolic, bismaleimide, cyanate ester, and thermoplastic resins, as wellas carbon and various metals, and other suitable matrix materials knownin the art. Those of skill in the art will appreciate that the types offiber materials and matrix materials are extensive and will furtherappreciate that any suitable fiber material and matrix material can beused, as appropriate for the intended application.

The composite material cell structure is formed by constructing a longlattice log, then slicing the log into sections of the appropriatethickness, such as 1 inch, and shape, such as planar or contoured. Eachslice becomes a separate lattice fin. The process for forming a latticelog is illustrated in FIG. 12. In the first step, a desired number ofmandrels 60 is provided in the desired cross-sectional shapes to formthe various cells of the cell structure. Square and triangular mandrelsare illustrated, but other shapes, such as rectangular, hexagonal,octagonal, or circular, or other segmented curved shapes can beprovided, as desired for the particular lattice fin configuration. Themandrels can be machined or extruded in an appropriate length. Squareextrusions can be machined to form triangular halves. Aluminum is asuitable material for extrusion processes. A machining process is moresuitable for steel or titanium. Extruded and/or machined plasticmandrels from materials such as polytetrafluoroethylene (PTFE) andmandrels cast from ceramics, salts and other initially fluid materialscan also be provided. Mandrel materials can be chosen to be dissolvableto remove them from the log after molding and curing. Soluble materialsinclude water soluble ceramics or salts. Aluminum can be dissolved withan aluminum solvent. Mandrels can also be made from silicone and othermaterials that expand considerably during heating to provide compactionforce during the curing process. The mandrels then shrink upon cooling,allowing the mandrels to be mechanically removed more easily.

Optionally, each mandrel is coated with a release agent to aid insubsequent mechanical removal of the mandrels from the part aftercuring. For example, the mandrels can be wrapped with a release tape 64,such as a PTFE tape, or sprayed or dipped in a release agent such as awax or wax-like material. The mandrels are then covered with thecomposite material. In one embodiment, the mandrel may be wrapped bylaying a fiber/resin prepreg fabric and/or broadgoods 66 of any suitableor arbitrary fiber arrangement over the mandrel in any desired number oflayers. In other embodiments, the material can be braided onto themandrel or filament wound onto the mandrel. The material can be aprepreg fabric, in which a resin for the matrix material has beencombined with the fibrous reinforcement and partially cured to a“b-stage” prior to application to the mandrel, and is subsequentlycured. Pre-impregnated composite starter materials aid the mandrelwrapping process because the matrix material, when slightly heated,becomes tacky and helps the fabric stick to the mandrels. Alternatively,the material can be dry and the matrix material infused subsequentlyinto the fibers.

The individual mandrels are assembled into a log assembly 68 having thedesired cell configuration. The log assembly of mandrels can beoverwrapped with an outer layer 70 of a composite material at this stagefor formation of the outer frame. Alternatively, the mandrels can bewrapped so that the outer cell walls define the frame. The assembly,with or without the overwrapping, is placed in suitable tooling assembly80 (see FIG. 13) to apply pressure and maintain the mandrels inalignment while the matrix material cures. The assembly is then cured ina suitable curing press or oven for a suitable duration or the toolingmay include internal heaters, as would be known in the art. If a dryfiber method such as braiding or filament winding is used to apply thefibrous reinforcement to mandrels or to form the outer frame, the matrixmaterial is infused into the log assembly prior to cure.

After curing, the log assembly 68 is removed from the tooling assembly80. A composite material to form the outer frame 14 can be placed aroundthe cured log assembly at this stage, if the outer frame was not formedpreviously. If necessary, any further curing may take place. Themandrels 60 are then pushed out or otherwise removed from the logassembly. Individual lattice fins 72 are sliced from the log in anydesired width. Alternatively, the mandrels can be left in place duringslicing and other finishing operations to help stabilize the thin cellwalls and removed later in the process after individual fin-slicing hasoccurred. As noted above, the outer frame 14 can alternatively be ametal frame. The metal frame can be attached to the composite cellstructure in any suitable manner, such as by curing of the matrixmaterial or with a suitable bonding adhesive.

In one suitable embodiment, the composite cell structure is formed froma plain weave fabric of carbon fibers pre-impregnated with epoxy resin.The fabric should be as thin as possible if minimizing the thickness ofthe cell walls is desired. For example, using a 1K tow fabric, eachmandrel can be wrapped with a single layer, resulting in a double-plycell wall thickness as little as 0.008 to 0.016 inch. A suitable 1K towfabric is commercially available from Aerospace Composite Products ofCalifornia. Other commercially available carbon/epoxy prepregs wovenwith a 3K tow result in a material that makes laminates with a cured plythickness of approximately 0.010 inch. Wrapping all mandrels with such afabric results in a cell structure having a wall thickness ofapproximately 0.020 inch. If the cell walls are desired to be formedwith a single ply, alternate mandrels can be wrapped. Similarly, ifwalls of greater thickness are desired, multiple plies or a heavierfabric can be used. It is also possible to tailor cell wall thickness bywrapping mandrels with different materials, so that the finished wallthickness becomes the total of the materials on facing mandrel surfacesin the final assembly.

FIG. 13 illustrates one suitable form of the tooling assembly 80 for thecomposite lattice fin. The tooling assembly includes a mold assemblyhaving pieces 82 arranged to form a cavity 84 of the desired final outerconfiguration. In the embodiment illustrated, a rectangular cavity isprovided. For a lattice fin with beveled corners, outer triangular shims86 can be provided to fill the corners of the mold cavity if the moldcavity is not formed with beveled corners. Alignment buttons 90,described below, maintain the mandrels in proper alignment in thecavity.

To aid in holding the mandrels in alignment in the tooling assemblyand/or to minimize twisting of the mandrels, an alignment fixtureassembly can be provided at each end of the log assembly. In oneembodiment, an alignment button 90 is provided on each end of eachmandrel. See FIG. 14. The buttons are preferably made from any suitablematerial, such as brass, and each button has the same cross-section asits corresponding mandrel. The dimensions of the buttons are preciselyoversized from their associated mandrels by the thickness of thematerial to be wrapped over the mandrel. After the mandrels are wrappedwith the uncured or partially cured composite, each end is plugged witha button, which can be friction fit or fastened to a counterbore in themandrel end in any suitable manner. When the mandrels are loaded intothe tooling assembly, the uncured or partially cured composite materialis compressed until the surfaces of the buttons come into contact withone another and the mold cavity surfaces and force the mandrels into aprecise alignment within the tool. This greatly improves alignment ofthe cell wall intersections, because each mandrel has a hard stop. Inaddition, the mandrels are restrained from rotation. Other approaches tomandrel centering are possible, including insertion of aligning pins 92into the end of each mandrel through an end plate or jig 94 withappropriately spaced holes. See FIG. 15. In cases where precise interiorgeometry is less important, the same general approach can be used withno special provision to maintain mandrel center-to-center location or torestrain rotation.

In an alternative embodiment, a vacuum bagging process can be used tocure the log assembly, eliminating the requirement to fabricate a hardouter tool. See FIG. 16. In this process, the log assembly 68 is placedwithin a bag 102 and a vacuum applied to draw resin through the fabric.Alternatively, a prepreg material can be used and the resin infusionstep avoided. The vacuum bag can be placed in an autoclave and theexterior pressure can be raised to aid in compacting the material andprevent fiber buckling. Alternatively, the same procedure can be usedwith a furnace operating at atmospheric pressure, without applyingadditional external compaction pressure beyond that created by drawing avacuum in the bag.

The mandrels and composite material can be laid up in a variety of otherways. For example, a layer of wrapped or unwrapped mandrels can be laidin a mold cavity, for example, angled to provide a row of diamondshapes, and a composite material laid over the surface of the row ofmandrels. A second row of mandrels, wrapped or unwrapped, can be laidover the composite material to compress the material into the anglesbetween the mandrels of the first row. By varying the compression of thematerial into angles and the number of layers of material, differentialwall thicknesses can be obtained. For example, it may be desirable toprovide greater wall thicknesses near the base of the lattice fin wherethe greatest stresses are encountered in use.

A further embodiment uses a unidirectional tape. The tape isadvantageous in that the cured ply thickness may be approximately 0.005inch per layer. This may be advantageous over broadgoods, because theorientations can be tailored to a desired direction of interest foroptimal strength and/or stiffness. The tape is typically slightlythinner than broadgoods, thus making it possible to use multiple layersper cell wall, rather than fewer layers per wall for broadgoods incertain applications and still obtain a low finished wall thickness.Using multiple layers allows an optimal amount of material to beoriented in the desired direction.

As noted above, the lattice fin also includes a base that enables thelattice fin to be mounted for pivoting motion to a body. The baseincludes a portion 17 for attaching to the frame and mounting fixtures19 for mounting to the body. It will be appreciated that the particularconfiguration of the base depends on the application and the desiredmounting arrangement to the fluid-born body. (See, for example, FIG.17.) The base can be formed of metal or of a composite material. Thebase can be formed in any suitable manner, such as by molding,pultrusion, hand-layup, extrusion, machining, or casting. If formed as apultrusion, extrusion, or other initially long continuous strip,individual bases can be sliced from a single long part. The basestructure may also be fabricated by machining using conventionalmachining techniques or through other processes such as laser cutting,water jet cutting, or electrical discharge machining. The base can alsobe formed of a composite material integrally with the lattice fin. Inthis case, appropriate tooling is provided and the composite material islaid up to form the desired base configuration, as would be known in theart.

When the base is formed separately from the cell structure and frame,the base can be attached to the fin in any suitable manner, such as byfurnace brazing, dip brazing, welding, or adhesive bonding. The base canalso be formed integrally with the outer frame. For example, the baseand outer frame can be cast as a single piece of metal.

The lattice fin typically requires a certain amount of finish machining,such as drilling and tapping of holes. In some cases, inserts may beused to reinforce the hole areas or provide other useful features, suchas spring deployment. The composite cell structure can be machined toprovide an aerodynamic shape to the leading and trailing edges, or thefin can be used with the as-sliced, square or contour cut ends. Thelattice fin is then attached to the desired missile or other fluid-bornbody.

The intended application influences the particular choice of lattice finembodiment and configuration. For example, when bomb bay doors open,there can be a high level of acoustic noise, subjecting the fins to asevere dynamic loading condition. The lattice fin walls must besufficiently robust to withstand this loading. The lattice fins may berequired to withstand operation at supersonic, subsonic, or transonicspeeds. In some applications, minimizing drag is important, whereas inother applications, minimizing drag is of less concern. Similarly, insome applications, the ability to operate at high temperatures isimportant, whereas in other applications, the temperature is of lessconcern.

Prior art lattice fins have been developed for use with missiles, bombs,or rockets. The lattice fin of the present invention is suitable forthese applications and can also be used with other fluid-born bodies.For example, the fins can be used on cargo canisters filled withemergency relief supplies that are dropped from aircraft. It can also beuseful for air-dropped sensor systems, and various ground-based,range-extended, rocket and gun-launched projectiles and missiles.Underwater applications that take advantage of the compact storage andlower control moments are also possible.

The invention is not to be limited by what has been particularly shownand described, except as indicated by the appended claims.

1. A lattice fin having an open cellular configuration providingaerodynamic surfaces for use on a fluid-born body, comprising: aninterior cell structure comprising an array of cells defined by cellwalls having a depth direction and open ends, the cell walls comprisingaerodynamic surfaces, having a leading edge and a trailing edge, forfluid flowing through the open ends and past the cell walls; an outerframe surrounding the interior cell structure about outermost walls ofthe cell walls; wherein the interior cell structure is formed of acomposite material comprising a fibrous reinforcement impregnated with amatrix material; and a base attached to the outer frame and configuredfor attachment to the fluid-born body.
 2. The lattice fin of claim 1,wherein the cells are formed of a single ply of the composite material.3. The lattice fin of claim 1, wherein at least a portion of the cellsare formed of multiple plies of the composite material.
 4. The latticefin of claim 1, wherein the cell walls have differing wall thicknesses.5. The lattice fin of claim 1, wherein the outer frame is formed of acomposite material comprising a fibrous reinforcement impregnated with amatrix material.
 6. The lattice fin of claim 1, wherein the outer frameand the cell structure are formed of a same composite material.
 7. Thelattice fin of claim 1, wherein the outer frame is formed of metal. 8.The lattice fin of claim 7, wherein the outer frame is formed ofstainless steel.
 9. The lattice in of claim 1, wherein the basecomprises an extrusion.
 10. The lattice fin of claim 1, wherein the baseis formed of metal.
 11. The lattice fin of claim 10, wherein the base isformed of aluminum.
 12. The lattice fin of claim 1, wherein the base isformed of a composite material.
 13. A lattice fin having an opencellular configuration providing aerodynamic surfaces for use on afluid-born body, comprising: an interior cellular structure comprisingan array of cells defined by cell walls comprising strips of metal, thecell walls having a depth direction and open ends, the cell wallscomprising aerodynamic surfaces, having a leading edge and a trailingedge formed by edges of the strips of metal, for fluid flowing throughthe open ends and past the cell walls, at least one of the leading edgeand the trailing edge of the strips of metal shaped to comprise anaerodynamic profile; an outer frame surrounding the cellular structureabout outermost walls of the cell walls; and a base attached to theouter frame, the base configured for attachment to the fluid-born body.14. The lattice fin of claim 13, wherein the cell walls have differingthicknesses.
 15. The lattice fin of claim 13, wherein the outer frame isformed of a composite material comprising a fibrous reinforcementimpregnated with a matrix material.
 16. The lattice fin of claim 13,wherein the outer frame is formed of a metal.
 17. The lattice fin ofclaim 16, wherein the outer frame is formed of stainless steel.
 18. Thelattice fin of claim 13, wherein the base comprises an extrusion. 19.The lattice fin of claim 13, wherein the base is formed of metal. 20.The lattice fin of claim 19, wherein the base is formed of aluminum. 21.The lattice fin of claim 13, wherein the base is formed of a compositematerial.